Trilithium aluminium trimolybdate(VI), Li₃Al(MoO₄)₃, has been grown as single crystals from α-Al₂O₃and MoO₃in an Li₂MoO₄flux at 998 K. This compound is an example of the well known lyonsite structure type, the general formula of which can be written asA₁₆B₁₂O₄₈. Because this structure can accomodate cationic mixing as well as cationic vacancies, a wide range of chemical compositions can adopt this structure type. This has led to instances in the literature where membership in the lyonsite family has been overlooked when assigning the structure type to novel compounds. In the title compound, there are two octahedral sites with substitutional disorder between Li⁺and Al³⁺, as well as a trigonal prismatic site fully occupied by Li⁺. The (Li,Al)O₆octahedra and LiO₆trigonal prisms are linked to form hexagonal tunnels along the [100] axis. These polyhedra are connected by isolated MoO₄tetrahedra. Infinite chains of face-sharing (Li,Al)O₆octahedra extend through the centers of the tunnels. A mixed Li/Al site, an Li, an Mo, and two O atoms are located on mirror planes.